Migrating Dynamic Disks

Question

I am migrating from a FC4700 and CX400 to a new CX3-40. Most of the hosts are windows servers with multiple luns presented to them that are then lumped together under a single dynamic disk. Some of the servers have over a TB made up of 4 or 5 LUNS all grouped together as one dynamic disk. Any recommendations on the best way to migrate these? We have purchased San Copy but I have yet to find any white papers that talk about migrating these luns at the same time to keep them consistent.

GlenH · Accepted Answer

SANCopy will definitely be faster than host mirroring...

A SANCopy migration is quite straight forward as long as you remember the following:

1. Ensure you copy all of the LUN's and ensure they are all copied at the same point in time. This means you need to shutdown the server at some point to do the final copy (if you are using incremental) or have the server shutdown for the entire duration of the copy if you are doing a full copy.

2. You must never present both copies of the LUN's to the server at the same time - as you are doing a block level copy, you will create exact duplicates of the volume ID's.. If you attempt to start the server when it can see both sets of disks, then you will have big problems..

So your basic plan is:

1. Setup your zoning for SANCopy (zone source and target SP's together)
2. Setup the LUN's on the target array (same size)
3. Ensure you have sufficient snap cache LUN"s on the source array
4. Create incremental SANCopy sessions of all your source LUN's on the source array (incremental push)
5. Perform a sync.

Now you've got most of the data there, during your change window, do the following:
6. Shutdown the host
7. Perform an incremental update for all the SANCopy sessions
8. Remove the hosts zoning from the source array (or take the host from the storage group)
9. Change the hosts' zoning etc. to point it to the target array and update the target array storage group
10. Boot the host.
11. It should all just come up as it was...

If you are not doing incrementals, then step 7 above would need to be a full copy.

One thing to look out for - if you are booting from the array, ensure the HLU of the boot lun is the same on both arrays (check that in the storage group properties)

Good Luck,
Glen.

bthessel-sRige · Answer

The only thing I would be worried about with the mirroring option is how long does it take more the OS to get the mirror built. Would it be worse than using SAN Copy?

gambit116 · Answer

You have multiple LUNS which makeup a Volume, I don't know if windows can piece togather your volume from the luns on the new Array. technically windows should be able to read the disk signature and put it back togather. I have never tested this and I would recommend you test this funtionality first.

To use san copy you will have definetly take a outage, to make sure you have a consistant point in time copy and making the File system switch to the new Array.

I have used OS based mirroring several times and had not had any real performance issues. you could setup a 100 Gb lun from each array and see how long it takes via san copy and mirroring and then extrapolate.

Can't really say which one is faster.

gambit116 · Answer

Ofcourse you should always make sure you have a good backup.

gambit116 · Answer

Did you consider Host based mirroring. I have done several migrations this way.

We present a Lun from the new array. setup windows mirroring. Once the disks are mirroredup we break the mirror and take away the old Disk.

Perform this during off times, to conserve your CPU and IO load.

GlenH · Answer

Hi SANguy,Windows Dynamic disks can be considered a restricted equivilent of veritas volume manager - the very first section of each disk holds identifiers that enable windows to just look at the group of disks and understand which other disks go with it along with the volume layouts, volume names etc..All you need to do is ensure that all of the disks are there and it will do the rest for you.Glen.

bthessel-sRige · Answer

Thanks everyone for your help. This was kind of what I was thinking to do but I wanted to make sure.

Allen Ward · Answer

It looks like you have your answer, but the one thing I would add in response to some of the suggestions is that you can't natively mirror dynamic spanned volumes on Win2K or Win2K3.

A spanned volume is what you get when you concatenate multiple LUNs together to get a bigger drive. Once you do this Windows won't let you mirror it. In the same way it restricts you from spanning additional space onto a striped drive. It's a limitation of the Operating System.

So... if you wanted to do something along the lines of host based mirroring you would have to use third party software to do it.

CockneyUSA · Answer

We've just done this, from FC4700s to a CX3-40 in the
last 7 days.

SanCopy is the way to go. Follow the EMC tech advice
for the process.

Just some important points. Incremental SanCopy does
not work from a FC4700. Incremental SanCopy has to
be done as a "push" copy, so the SanCopy software has
to be installed on the source array. It will work on
the cx400 if the flare code is at the correct level.

We used the SanCopy "pull" to the cx3-40 and took the
outage window necessary.

As far as time goes, we were going over a 1Gb link
between arrays and by migrating four luns at a time
(2 on SPA and 2 on SPB) we got up to 520GB per hour.
This slowed to about 180GB/ph when copuing single
LUNs.

We also made sure that when we added the new LUNS to
the storage group we set the Host ID to match the
original LUNs.

All went smoothly.

CockneyUSA.

Did you run through the admhost commands, etc. that they recommend or did you just shut down the host to do the migration. I'm trying to keep this as simple as possible so if I can just shut down the host, do the copy, change the zoning and bring the host back up that would be great. The admhost stuff doesn't appear complicated just extra steps.

EKellerman · Answer

--'Just some important points. Incremental SanCopy does not work from a FC4700. Incremental SanCopy has to be done as a 'push' copy, so the SanCopy software has to be installed on the source array.'Cockneyusa are you 100% sure about that incremental not working on a FC4700? Our EMC advisor scheduled SAN Copy and SnapView to be installed so we could proceed with a migration in this fashion.Knowledgebase article emc79323 indicates that as long as you have San Copy 2.0 you can 'push' from a FC4700 incrementally.:'Not all CLARiiON arrays are qualified to run SAN Copy 2.0 software. Only if the source LUN is on one of these CLARiiON arrays is it possible to incrementally push changes from a source LUN to a target LUN: - CX400, CX500, CX600, and CX700 arrays - FC4700 and FC4700-2 arrays Only if the source LUN is on one of these CLARiiON arrays is it possible to ¿incrementally¿ push changes from this source to a target LUN. '

CockneyUSA · Answer

You are correct about SanCopy 2.0 (and we have that). It will do an incremental copy, but not to a CX3-40. The flare codes are too far apart. In fact we even tried a full "push" copy from the FC4700 and it doesn't even see the CX3-40 as a target.

I must say that we are on flare code 24, but I think flare code 22 is the same. Between cx arrays you can go n-1, that is flare 16 can copy to flare 22.

From emc143933:

"While it is always recommended that both the SAN Copy array (CX3-Series array in this case) and the remote array (CX600 array in this case) be at the latest FLARE revision, one FLARE revision lower (N-1) is supported for CX-Series arrays. FLARE Release 19 is the most recent release for the CX600 array. Therefore, FLARE Release 16 (which is the previous revision) is supported for SAN copy."

Hope this helps.

CockneyUSA · Answer

No, we didn't use the admhost commands. These are only necessary on a running machine to cleanly remove the LUNs. We don't want to remove the LUNs, we just want them in a different place when the host reboots. rezoning and adding them all to the new storage group achieves this.

bthessel-sRige · Answer

We've just done this, from FC4700s to a CX3-40 in the
last 7 days.

SanCopy is the way to go. Follow the EMC tech advice
for the process.

Just some important points. Incremental SanCopy does
not work from a FC4700. Incremental SanCopy has to
be done as a "push" copy, so the SanCopy software has
to be installed on the source array. It will work on
the cx400 if the flare code is at the correct level.

We used the SanCopy "pull" to the cx3-40 and took the
outage window necessary.

As far as time goes, we were going over a 1Gb link
between arrays and by migrating four luns at a time
(2 on SPA and 2 on SPB) we got up to 520GB per hour.
This slowed to about 180GB/ph when copuing single
LUNs.

We also made sure that when we added the new LUNS to
the storage group we set the Host ID to match the
original LUNs.

All went smoothly.

CockneyUSA.

Did you run through the admhost commands, etc. that they recommend or did you just shut down the host to do the migration. I'm trying to keep this as simple as possible so if I can just shut down the host, do the copy, change the zoning and bring the host back up that would be great. The admhost stuff doesn't appear complicated just extra steps.

bthessel-sRige · Answer

I wanted to thank everyone for their help. I have completed doing the migrations and it worked flawlessly. I shut down the server, migrated the LUNs, put the server and LUNs in a new storage group on the new array, started up the server and everything was perfect. Thanks again to everyone.

CLARiiON

Migrating Dynamic Disks

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